1. Field of the Invention
The invention relates to a load positioner.
2. Description of the Prior Art
In the handling of a number of packages, boxes, or other objects, a common task is to manually transfer them between an elevated table, conveyor, shelf, or other location, and a pallet resting on the floor. While the shelf, for example, remains at a fixed height, the top of the load on the pallet, where the next box or object is to be placed or removed, usually is at a different height which varies as the packages, etc., are piled on or removed from the pallet. This difference in height, and the changes in this difference during loading or unloading of the packages, can be fatiguing for the person doing the moving. Therefore, pallet positioners, also known in the art as load elevators, have been developed for raising the pallet from the floor to a more convenient height and even for automatically adjusting the height of the pallet as the load increases or decreases, so that the preferred height of the top of the load is maintained.
U.S. Pat. No. 5,299,906 discloses a self-adjusting pallet positioner supported by a scissors linkage located under a rotatable load platform. The vertically expandable scissors linkage is coupled to an air-actuator chamber that includes a compressible bellows and a fixed-volume reservoir placed under the load platform. The bellows is compressible between specified maximum and minimum bellows heights which correspondingly determine substantially different maximum and minimum bellows volumes. The air reservoir is coupled to the bellows and has a fixed volume that is substantial compared to the difference between the maximum and minimum bellows volumes. As a result of this configuration, the pallet positioner exhibits very good self-leveling characteristics.
In the positioner's unloaded condition, the scissors linkage is extended and the platform is situated at a convenient level for loading packages and/or materials onto a pallet placed on the platform. As boxes or crates are stacked on the pallet and the weight and height of the stack on the pallet increase, the scissors linkage and the air bellows automatically contract under the load and the platform sinks approximately in proportion to the height increase of the stack for uniform loads. Thus, the top of the stack is maintained at a roughly constant level by the self-leveling feature and the stacking process is facilitated. The rotary design of the platform also helps ease the stacking process since the platform can be rotated to place boxes or crates next to one another as necessary.
When the pallet is fully loaded, it is removed from the platform with a fork lift. At this time, the platform is in its lowest position.
A low-profile pallet positioner which addresses these problems is disclosed in U.S. Pat. No. 5,782,602. The positioner of this patent consists of an upright housing and a pair of spaced, parallel outriggers extending from the housing. Vertical guide rods are mounted on the exterior of the housing and a cantilevered platform assembly with a rotatable platform is movable over the outriggers up and down along the guide rods. In its lowermost position, the platform assembly sits on the ground between the outriggers, thereby permitting the placement of a pallet truck under the pallet. The cantilevered platform assembly is driven by a cylinder-and-piston unit which is disposed inside the upright housing and engages the periphery of the assembly through a slot in a wall of the housing. The cylinder-and-piston unit is extended and retracted by a power unit consisting of a motor, pump and tank likewise disposed inside the housing, and the platform is raised and lowered as needed by the operation of the power unit.
Inasmuch as the platform is rotatable, care must be exercised in removing the pallet from the platform. Furthermore, if the operator of the pallet positioner is inattentive or distracted when the platform approaches its lowest position, the operator may position herself or himself with her or his feet below the platform. The operator's feet could then become trapped between the platform and the ground.
A strip-like conductor, extending along the top of each outrigger, is provided to prevent injury to the operator. In addition, if a pallet becomes misaligned as the platform descends, the pallet may strike one or both of the strip-like elements, thereby deactivating the power unit so that tipping of the pallet can be avoided.
Several vertical shafts are slidably mounted on the platform assembly below and circumferentially of the platform. The upper end of each shaft is provided with a layer of rubber or the like and, when the platform assembly is in a raised position, the rubber layers are separated from the platform by a gap. On the other hand, the lower ends of the shafts project below the platform assembly. As the platform assembly approaches its lowermost position, the lower ends of the shafts contact the ground thereby causing the shafts to move upwards relative to the platform. The rubber layers on the upper ends of the shafts then come into contact with the platform so that the platform is prevented from rotating. Although this braking system is generally satisfactory, there can be a loss in braking effectiveness if the rubber layers or the lower ends of the shafts undergo wear.
A photoelectric arrangement is provided at the ends of the outriggers remote from the housing. The photoelectric arrangement includes a photoelectric cell at the remote end of one outrigger and a light source at the remote end of the other outrigger. The light source directs a beam of light towards the photoelectric cell and, when the platform is traveling downward and the light beam is broken by an object placed in the path of the beam, the platform stops. This prevents the foot of an operator from becoming trapped beneath the platform if the operator should place her or his foot between the light source and the photoelectric cell. While this safety system operates well, it fails to protect an operator who places her or his foot below the platform at locations other than those between the remote ends of the outriggers.